Glial cells form intimate contact with neurons and help orchestrate brain wiring during development and facilitate neuronal functions in adulthood. Therefore, it is important to elucidate glial functions in vivo. However, highly specific and adaptable mouse lines for studying two major glial cell types, mature astrocytes and NG2 cells are still lacking. Here we propose to create mouse genetic tools that would allow one to probe into the function of these two types of glial cells in a temporally controllable fashion. The proposed Tet-OFF binary system consists of two groups of mice: 1) driver lines that express tTA in specific types of glial cells; 2) effector lines that express transgenes for cell ablation or transcriptomic profiling under the control of Tet Operon (TetO). The system would allow one to pick and choose individual driver and effector lines to study a specific problem in glial biology. When combined with existing Cre lines, intersectional genetics can provide unprecedented cell type-specificity to analyze glial functions in vivo. Although apparently straightforward, problems of leakiness, variegation/mosaicism, and silencing of transgene expression could derail such efforts. With careful preparation, our lab is now ready to take on this challenge. With our extensive experience with ES cell-based knock-in strategy gained from creating and optimizing a mouse genetic mosaic system, we will use carefully designed targeting strategies to ensure the faithfulness and completeness of transgene expression. As importantly, we have broadly consulted with leaders in the field of glial biology and mouse genetics, and will target these transgenes into the most promising genomic loci for faithful and specific transgene expression. We believe that genetic tools described in this grant will have a broad impact on studying the roles of glial cells for normal functions and diseases in the central nervous system. For example, RNA tagging in astrocytes or NG2 cells will allow one to study the transcriptional landscape of these cells throughout the normal development or under certain pathological conditions. Cell ablation experiments could help reveal the critical contributions of specific glial cell types in brain wiring during development and cognitive functions in adulthood. Applied to brain tumor research, cell ablation will help identify important cellular targets for effective therapeutic intervention. Lastly, principles learned from the proposed work will provide a firm foundation for the successful expansion of the system in the future to address a diverse range of exciting topics in neuroscience.